Gearshift transmissions of motor vehicles are usually controlled or shifted by means of an actuating device arranged within reach of the driver. As a rule actuating elements such as shift levers or selector levers are used, which are for example arranged between the front seats of the motor vehicle.
The design and ergonomic requirements for such actuating devices or selector levers for gearshift transmissions are many and various. For example, in order to give the driver a realistic feeling of transmission actuation for reasons of safety and ergonomics, such actuating devices are required to provide the driver with both visual and sensory or tactile feedback about the current shift or operating status of the transmission.
Depending on the status of the gearshift transmission to be operated and depending, too, on other motor vehicle status factors—ignition switched on, engine running, vehicle speed, etc.—it is for example generally necessary, sometimes, to restrict the actuation range of the selector lever so as to prevent the driver from selecting any momentarily inadmissible shift conditions or drive settings of the gearshift transmission.
Particularly in the case of gearshift transmissions controlled by shift-by-wire, including most of the automatic transmissions in use today, for reasons of safety and ergonomics it is necessary for momentarily inadmissible shift conditions to be signaled to the driver both visually and by touch, by appropriately locking the associated operating positions of the selector lever.
In the case of the previously usual, purely mechanical transmission actuation or mechanical coupling between the selector lever and the gearshift transmission —for example by means of a cable or rods—by virtue of this mechanical coupling between the selector lever and the transmission the position of the selector lever always reflected the actual status of the transmission, and any actuation blocks in the transmission could be directly felt at the selector lever as well owing to this mechanical transfer.
However, in the case of the increasingly used electric actuation, or that of shift-by-wire actuation of gearshift transmissions, there is no longer any mechanical coupling between the actuating element or selector lever in the passenger compartment and the transmission of the motor vehicle in the engine compartment. Rather, in the case of “shift-by-wire” transmissions shift commands are usually transmitted from the actuating device to the motor vehicle's transmission exclusively by means of electric or electronic signals, with subsequent, usually electro-hydraulic implementation of the shift commands in the transmission itself. This applies in part to modern gearshift transmissions, but in particular to the current generations of automatic transmissions, most of which are actuated completely remotely by actuators.
However, in the case of gearshift transmissions actuated by shift-by-wire the result of this lack of any mechanical link between the transmission actuator system and the selector lever is that any shift locks engaged in the transmission—because of the current status of the vehicle or its transmission—can no longer react via a shift rod upon the condition of the selector lever. Accordingly, no longer can the driver recognize with certainty, by virtue of the blocking of certain shift positions detectable at the selector lever, that the corresponding drive settings or transmission conditions are not permissible and cannot be selected while in the driving condition at that time.
It has been attempted to overcome this problem by providing the selector levers of shift-by-wire controlled gearshift transmissions with various actuators for the selective blocking of inadmissible shift commands. These actuators are activated depending on the status of the vehicle or its transmission, in order to restrict the original overall movement range of the selector lever as appropriately for the momentary driving or transmission status.
However, this is disadvantageous because the structural space that must be provided in the area of the selector for such a plurality of actuators is not always available. Furthermore, such usually electromagnetic actuators, which contain copper windings of not inconsiderable weight, contribute toward an undesired increase of the weight of the shift unit as a whole. Not least, a plurality of separate actuators also increases the assembly effort and hence the costs for the shift unit. And in view of the increased efforts to reduce fuel consumption, even the energy consumption of such actuators and the associated generation of heat play a part that is not negligible.